Sheet clamping means for polishing machines



June 5, 1951 CHAPLIK 2,555,317

SHEET CLAMPING MEANS FOR POLISHING MACHINES Filed March 15, 1950 '7 Sheets-Sheet 1 June 5, 1951 CHAPUK 2,555,317

SHEET CLAMPING MEANS FOR POLISHING MACHINES Filed March 15, 1950 'r Sheets-Sheet 2 June 5, 1951 R. CHAPLIK 2,555,317

SHEET CLAMPING MEANS FOR POLISHING MACHINES Filed March 15, 1950 7 Sheets-Sheet 3 Ja/rzzor'. 2 6 z'm 654714;)?

June 5, 1951 R. CHAPLIK 2,555,317

SHEET CLAMPING MEANS FOR POLISHING MACHINES Filed March 15, 1950 7 Sheets-Sheet 4 SHEET CLAMPING MEANS FOR POLISHING MACHINES Filed March 15, 1950 7 Sheets-Sheet 5 June 5, 1951 R. CHAPLIK SHEET CLAMPING MEANS FOR POLISHING MACHINES 7 Sheets-Sheet 6 Filed March 15, 1950 II! 1: -57 3 Ix A. Ni

June 5, 1951 R. CHAPLIK 2,555,317

SHEET CLAMPING MEANS FOR POLISHING MACHINES Filed March 15, 1950 7 Sheets-Sheet '7 Patented June 5, 1951 SHEET CLAMPING MEANS FOR POLISHING MACHINES Rubin Chaplik, Chicago, Ill.

Application March 15, 1950,Serial No. 149,771

14 Claims. 1

Large stainless steel sheets are commonly polished in machines provided with reciprocable beds on which the sheets are laid and carried back and forth underneath an endless belt coated with an abrasive; the sheets being firmly anchored to the bed by clamps at one end of the sheets. Obviously, the areas gripped by the clamps cannot receive a polish and must be out off at the end of the polishing operation. Thus there is a waste of material and the cost of the final product is further increased by the amount that it costs to do the trimming.

The primary object of the present invention is to eliminate such waste and expense as is incurred in said prior practice due to the necessity of trimming polished sheets to remove portions that could not receive a polish.

Since clamps of some sort must be used to hold stainless steel sheets in place in the polishing machines, the present invention may also be said to have for its object to create a novel and efficient clamping system for such sheets and, indeed, sheets of any other material, in a manner to expose the entire surface of each sheet to the action of the polishing member.

In carrying out my invention I employ power operated clamps and a control system that causes them to be manipulated in such a manner that each sheet is at all times effectively anchored, and yet each end thereof can be drawn freely through the polishing zone to permit every part of the face of the sheet to receive a polish.

Therefore, the present invention may be said to have for an object a novel method of handling a sheet so that no unpolished areas are left where clamps have been applied.

The various features of novelty whereby the present invention is characterized will hereinafter be pointed out with particularity in the claims, but, for a full understanding of the invention and of its objects and advantages, reference may be had to the following detailed description taken in connection with the accompanying drawings, wherein:

Figure 1 is a front view of a conventional sheet polishing machine having thereon attachments embodying the present invention in a preferred form; Fig. 2 is a section on line 22 of Fig.2; Fig. 3 is a View, on a larger scale, of a fragment of the rear side of the machine, showing the automatic switches and actuators in different relative positions than those occupied in Fig. 2; Fig. 4 is a top plan view of so much of the machine as is shown in Fig. 3; Fig. 5 is a view, on a larger scale than Fig. 2, showing only the right hand end of the machine; Fig. 6 is a front elevational view of the parts as they appear in Fig. 5; Fig. '7 is a section on line 'l-l of Fig. 5; Fig. 8 is a section on line 8-8 of Fig. 5, but on a larger scale; 9 iS a e n the same scale as Fig. 8, on line 9-9 of Fig. 5; Fig. 10 is a section on line I0-l0 of Fig. 5; Fig. 11 is a View, similar to Fig. 1, on a larger scale and showing only that part of the machine in which the left hand clamp means are located; Fig. 12 is a transverse, vertical section on a plane corresponding to line l2 l-2 of Fig. 11, with only the parts at the front of the machine being shown; Fig. 13 is a section on line l3l3 of Fig. 11; Fig. 14 is a section on line l4-l4 of Fig. 11; Fig. 15 is a section on line I5I5 of Fig. 12; Fig. 16 is a wiring diagram; Fig. 17 is a diagram showing the pneumatic clutch actuators, pneumatic cushions and the pipe and hose system associated therewith; and Fig. 18 is a more or less diagrammatic view of a hose connection between a stationary compressed air reservoir and cylinders on the re'ciprocable bed of the machine.

The machine shown in the drawing is a conventional one and will be described only briefly. It comprises a horizontal frame or base I that may be thirty five or forty feet long. On top of this frame or base are a plurality of parallel 1ongi-tud'inal beams 2, 2 on which a sheet-supporting' bedis mounted for sliding movements lengthwise of the machine. This bed comprises a short rigid panel 3 underlying and attached to one end of a long metal plate or thin panel 4. The combined lengths of the two bed members being about one half the length of the machine. Midway between the ends of the base structure is a high, heavy cast metal frame 5 that supports a wide, endless polishing belt 6. This belt embraces a group of four horizontal, parallel transverse rollers l, 8', 9 and Ill. Roller 1 lies near bed plate 4, roller 9 is directly over and far above roller 1, and rollers 8 and in are at intermediate levels, one to the left and the other to the right of rollers I and 9. The supporting structure for the belt rollers is open in front (the side toward the observer in Fig. 1), to permit the belt to be applied to or removed from the rollers by moving it through the front lengthwise of the rollers; a detachable plate H, shown in Fig. 1, spanning the distance between the base portion of the machine and the depending arm l2 that supports the front end of roller I. The belt is rotated and the bed reciprocated by power derived from a suitable driving means [3 that includes a motor i3 and a belt l3 which transmits power from the motor to the machine.

The apparatus that constitutes the present inention will now be described.

As best shown in Figs. -9, there rests slidably on the work-supporting bed, namely on that part of plate member 4 that overlaps rigid part 3, a heavy transverse plate M. This plate slopes down at its inner or left hand end, as at M and there terminates in a lip I4 of uniform thickness. A sheet I5 of cushioning material, of the same thickness as the lip, covers the bed for any desired distance from the edge of the lip toward the left. Blocks l6, l6 are secured to the under side of plate [4, adjacent to the ends of the latter, and outwardly from the edges of plate 4; these blocks being attached to piston rods l8. These piston rods are, in turn, attached to pistons [9 in cylinders 28. There are two of these cylinders arranged with their axes longitudinal of the machine, one on the front side and the other at the rear. These cylinders are close to a transverse shaft or rod 2| mounted in part 3 of the bed, and they are provided with sleeves 22 fixed thereto and rotatably embracing the rod or shaft. This makes it easy accurately to position the cylinders.

Plate [4 constitutes the lower jaw of a single or multiple clamp. In the arrangement shown there are, in effect, five clamps, each of which comprises an individual upper jaw 24 in cooperation with the corresponding part of plate l4. These upper jaw members are supported by transverse pivot pins 25 near the line at which the downward slope begins; providing each with a short nose portion 24 that tapers to a thin edge, together with a long tail portion 24 Mounted on the tail portion of each upper jaw member is an upright cylinder 26, containing a slidable piston 2'! which is connected to a piston rod 28 that extends out through the bottom of the cylinder, through a hole 24 in jaw members 24, and into a hole 29 in an arm 29 fixed to plate l4 and extending outwardly under member 24. A pin 30 connects the piston rod to arm 29 and allows the rod to rock a little as the tail of jaw member 24 moves up and down. A sheet A to be polished may be laid on the bed, with a marginal portion at the outer or right hand end resting on lip 14 and the upper jaw members 24 closed down upon it as shown in Fig. 8.

The clamping mechanism for the inner or left hand end of the sheet to be polished is shown in the general views, Figs. 1 and 2 and, in detail, in Figs. 11-15. This mechanism includes a single clamp that extends across the width of the machine to the left of the lower belt roller 1, namely, to the left of the polishing zone. This clamp consists of a wide, flat shoe 32, above the reciprocatory bed 4, and an anvil 33 that underlies the table below the shoe; the anvil being in the form of a sturdy bar. It should be noted that in this type of machine the beams 2, 2 are cut away in the region of the polishing zone, thus leaving room for the anvil 33. As best shown in Figs. 11, 12 and 13, a rod 2 connects together the separated ends of each divided beam; these rods being near the under edges of the beams.

In order to support the shoe and the anvil, I mount on the frame 5, above the ends of the shoe, a pair of slidin plates 35. As the supports at the front and the rear are preferably alike, I shall describe only one of them in detail. As best shown in Fig. 11, the overhanging front side of frame 5 has a downward projection 4 or lug 5 that is a little to the left of part 12, shown in Fig. 1. Underlying, and fastened at one end to this lug, is a thick plate 36 of considerable length arranged parallel to the longitudinal center of the machine. Between plate 36, at its other end, and the overhanging part of frame 5 is a spacer 31. A screw 38, passing through plate 36 and the spacer into the frame, completes the mounting of plate 36. This plate is cut away on the under side to create an undercut channel 39 into which plate 35 slidably fits. Secured to the under side of the latter plate is a plate 40 on the under side of which are a pair of spaced, parallel rails 4|, 41 that extend crosswise of the machine. These rails are L shaped and have their horizontal web or flange portions directed toward each other. Resting on and supported by the horizontal flanges of these rails is a sliding plate 42, which can be withdrawn by sliding it forwardly along the rails. Underneath plate 42, and fixed thereto, is a vertical cylinder 44. Within the cylinder is a piston 45 provided with a piston rod 45 that extends down through the lower end of the cylinder. On the lower end of the piston rod is a block 4? that contains a bearing 48 into which extends a trunnion 49 on the end of shoe 32. The trunnion is normally held in the bearing by a screw 58 that passes through a washer 5| longer than the diameter of the trunnion, and into the trunnion. As long as the screw 50 1s in place, the supporting slide 42 cannot be slid off the supporting rails therefor. A U-shaped hanger 52 depends from sliding plate 42, its arms being welded to lugs 54, 54 on the under side of that plate. This hanger embraces cylinder 44, and bearing block 41, and extends down below the latter far enough to receive within the same the adjacent end of the anvil member 33.

Beside the left hand half of the stationary plate 35, and fastened thereto, is a long cylinder 55 the axis of which is parallel to the longitudinal center line of the machine. In this cylinder is a piston 55 provided with a piston rod 5! that extends out through the right hand end of the cylinder and is fixed to a bracket 58 mounted on the right hand end of longitudinally slidable plate 35.

In order to keep dust from entering the cylinder 44, a flexible protecting sleeve 59, spanning the variable distance between the lower ends of the cylinder and the respective bearing block 41, is placed around the piston rod.

The air connections, to control the supply of air under pressure to the various cylinders will now be described.

Each of the cylinders 26 associated with one of the clamps at the right hand end of the machine has a hose connection 60 at the top and a similar connection 6| at the bottom. All of the hoses 60 are connected to manifold 62, while the hoses 6| are connected to a manifold 63. Both manifolds are connected to a conventional electromagnetically operated valve 64 that has two positions in each of which it remains until positively moved into the other position; this valve receives air from a supply pipe 55; air being admitted to each manifold at the same time that the other is connected to the atmosphere. The supply pipe preferably contains a device 66 to introduce a lubricant into the incoming air. Hoses 6?, 61 lead directly from the supply pipe to the right hand ends of cylinders 20, independently of valve 64. There is also provided a switch containing two push buttons '68 and (it (see Fig. 5) to provide for manual control of valve 64.

Because the air cylinders on the right hand end of the reciprocable bed travel through long distances, I have provided means to take up and pay out a flexible conduit as the bed reciprocates. Thus, as shown in Fig. 18, a long, flexible hose 59 may connect supply pipe 65 with a tank ill that contains compressed air. The hose runs over a pulley H suspended from one end of a cable 72 that extends over two pulleys, M and 14, and then downward, with a counterweight i5 fastened to its second end. When the bed is at the right hand end of its movement, pulley H is high up and the counterweight is in its lowest position. As the bed travels toward the left it pulls on the hose and flattens the loop therein, with the counterweight rising and the pulley H descending. The reverse action takes place on the return movement of the bed.

Air under pressure is delivered to both ends of cylinders 44 through a valve 16 similar to valve 64; hoses Ti and 18 leading from valve 16 to the upper and lower ends, respectively, of these cylinders. Hoses T9, 19 supply air directly to the left hand end of cylinders 55, 55 in much the same way as is done in the case of cylinders 2t, 29 which are supplied through hoses 61, 51; except that, as will be explained later, the air so supplied must be at a low pressure. air may also be supplied at will into the right hand ends of cylinders 55 through a hose section 81] connected to the high pressure tank and a section 8i that is connected to the right hand ends of these cylinders. These two hose sections are normally uncoupled, section 35 opening the right hand ends of the two cylinders to the atmosphere. The coupling parts 82 and 83 between these two hose sections, is of the type that automatically opens communication between these hoses, upon coupling, and, upon uncoupling, shuts on section 8% to prevent escape of air therefrom.

As has heretofore been explained, plate It that forms the lower jaw of the right hand clamp, is mounted on the bed so as to have a limited movement thereon, lengthwise of the machine. Movement in one direction, against the resistance of the air in cylinders 2.0, 26', is effected as follows: on the front end of plate M is fixed a lug 85 that projects forwardly. On the stationary base strucr ture of the machine, a little to the right of the polishing zone, is fastened a sturdy bar or stop 86. When the machine is in operation, lug 85 strikes the stop bar before the right hand clamp quite reaches the polishing zone when moving to the left. If the clamp is open when this occurs, the entire clamp stops while the bed continues its movement toward the left.

It is only necessary, therefore, to cause the moving bed to operate suitable switches to open and close the right and left hand clamps in proper time relation to permit both ends of a sheet to pass completely through the polishing zone, with nothing in the way to prevent complete polishing thereof.

This latter part of the invention is illustrated in Figs. 2-4; 87 and 3% representing two selfopening switches mounted on the rear side of the stationary base of the machine to the left of the polishing zone, and 89 and 91 being actuators or trippers for these switches, respectively. Switch 81 is located a little to the left of switch 88 and somewhat farther away from the rear face of the base. The switches have rockable lever arms 91 and 92, respectively, that normally are upright High pressure and are capable of swinging to the right and to the left. The switch trippers are mounted on a horizontal bar 94 supported on and extending lengthwise of the bed of the machine, a little above the level of the switches. Element is simply a little block or lug mounted on the bar, whereas element 89 is an elongated shoe carried by a bracket 95 which is mounted on the bar. The parts are so located that tripper 90 engages and moves switch arm or lever 92 in the same direction as that in which the bed is traveling at the time that the tripper engages that arm or lever. The same is true with respect to tripper 89 and arm or lever 9|.

The parts are further so proportioned that, as the bed moves toward the left from the loading position illustrated in Fig. 2, tripper 89 operates switch 87 which controls the left hand clamp and causes this clamp to close on the bed and overlying sheet before switch 88 that controls the right hand clamp is operated. Then switch 88 is operated to cause the right hand clamps to open. All of this must be done before the lug 85 on the clamp plate I l strikes stop bar 86. As soon as the left hand clamp closes, it is carried along bodily with the bed against the resistance of the air cushion in cylinders 55,- 55 which, of course, is transmitted to the bed. When lug 85 strikes stop 86, the right hand clamp stands still while the bed continues its movement-against the resistance of the air cushions in cylinders 20, 20. When the bed reverses itself and starts back toward the right, switch 38 is operated ahead of switch 87, so that the right hand clamps close again before the left hand clamp reopens. By this time lug 85 has left stop 86, so that the work is again being gripped by the right hand clamp before it is released by the other clamp.

The reason for making tripping element 89 in the form of a long shoe is to provide a longer time interval between the operation of the two switches when the bed is moving toward the left than when the movement is toward the right; one end of the shoe serving during movement of the bed toward the left to operate its switch a little before the right hand clamp strikes stop 86; while the other end of the shoe comes into action only after the bed has moved back toward the right far enough to make the position of the right hand clamp relative to the bed the same as it was before that clamp reached the stop. In other words, the left hand clamp opens right after the right hand clamp closes, on the return movement of the bed.

In order to avoid dragging wires and cables, I mount within the base of the machine three parallel wires 9'1, 98 and 99, near each other and extending longitudinally of the machine. On the under side of the bed I mount three trolley wheels I59, one on each wire. These wires being energized, the trolley wheels carry the current to the electromagnetic valve M, regardless of the position of the bed.

The system of air distribution may, perhaps, be better understood from the diagram, Fig. 12 The right hand part of the diagram contains only one element not heretofore mentioned, namely, a hand valve [ill somewhere in the connection between tank and valve The left hand portion of the diagram shows a conduit that contains a hand. valve i at, running from tank is to valve it. The connections between valve l6 and cylinders bear the same numbers in the diagram as in the other drawings. A feature that has not yet been explained is the use of an auxiliary tank or reservoir I85 to supply cushioning air to cylinders 55. The main air supply is at high pressure, preferably greater than one hundred pounds per square inch, whereas air under a pressure of not more than about twenty five pounds is preferable for cushioning purposes alone. Therefore, I connect the hoses 19 to the auxiliary tank and connect that, in turn, to supply conduit I02, with a reducing valve I06 interposed in the latter connection. Hose an is connected directly to the high pressure conduit so that, when hose sections 88 and 8! are coupled together, the pistons in cylinders 55 can be forced back, (toward the left in Fig. 11); the auxiliary tank readily absorbing the air forced out of such cylinders, without objectionable increase in pressure in the low pressure system.

In Fig. 16, the wiring diagram, I81 represents a transformer to provide low voltage current for the operation of the control system. The mid point on the secondary of the transformer is grounded through a manual switch H38. One main terminal of such secondary is connected by wire I09 to the movable member 8'! of double throw, self opening switch 87, while the other terminal is connected to the movable member 88' of the similar switch 88 by wire H8. Wire H8 is also connected to a wire II! that leads to push buttons 68 and 68% Push button switch 68 is connected to trolley wire 97 by a wire I I2, while switch [58 is connected to trolley wire 93 by wire H3. Trolley wire 99 is grounded. The two stationary contacts 81 and 8'! of switch 81 are connected to the solenoids 76 and 16 that operate valve 16, by wires H4 and H5, respectively. The remaining terminals of these two solenoids are grounded. The two stationary contacts 88* and 88 of switch 88 are connected to trolley wires 9'! and 98, respectively. The two solenoids 66 and 64' that operate valve 64 each is connected to the trolley wheel I!) running on the grounded trolley wire 99 and to a trolley wheel on one of the other of these wires.

The operation of the machine will now be de scribed briefly.

With the machine idle, the bed at the right hand end of the machine as viewed in Figs. 1 and 2. and the clamps open, a sheet A to be polished is laid on the bed with one end resting on lip M of clamp member M, as shown in Fig. 9. With switch I08 closed, push button 68 is then pressed and the clamp is closed on the sheet. The machine is then started, the bed moving toward the left and carrying the sheet under the revolving polishing belt. When the right hand clamp reaches stop 86 it can go no farther, but it must be open at that time to allow the bed to continue its movement. Therefore, before this clamp meets the stop, the left hand clamp must come into action and clamp the sheet to the bed. It has already been explained how the little switches 81 and 88 and their trippers bring the left hand clamp into action and then cause the right hand clamp to open before it reaches the stop. The trailing end of the sheet therefore passes completely through the polishing zone.

The bed automatically reverses its direction of travel in the usual manner, with the open right hand clamp remaining at rest for some time, due to the air pressure in cylinders 20. This allows the advancing end of the sheet again to ride up onto the lip on clamp member I4. As soon as is feasible after this occurs, switch 88 is operated to cause the right hand clamp to close. The operation of switch 81 may then follow immediately,

causing the left hand clamp to open. The conditions now existing do not change while the bed completes its movement to the right and again reverses itself and starts back toward the left; the operations of the switches 81 and 88 just described being repeated thereafter during each cycle constituting a round trip of the bed; and the polishing operations continuing until the machine is stopped.

It will be seen that the switches need remain closed only momentarily for, after a solenoid has shifted a valve, that solenoid may be deenergized; the valve retaining its position until the companion solenoid is energized to shift it back into its other position.

When the polishing of a sheet has been completed the machine is stopped and, upon pressing push button 68*, the right hand clamp opens and the sheet can be removed.

When the polishing belt is to be placed in the machine or be removed, the screw 50 (see Fig. 13) is unscrewed and forward cylinder 44, along with its supporting plate 42, may be removed by sliding it forwardly out of the machine.

In the event that it is desired to move the left hand clamp toward the left, and farther away from the polishing zone, hose sections and BI need only be coupled together to cause high pressure air to enter the right hand ends of cylinders 55. Since the air in the left hand ends of these cylinders is only under low pressure, the pistons 45 in these cylinders will be driven toward the left hand ends of the cylinders, carrying the cylinders 44 and plate 42 along with them. Upon uncoupling these hose sections, the pistons 45 return to their normal positions because the high pressure air in cylinders 55 has escaped to the atmosphere.

If, instead of large sheets, it is desired to polish one or more strip-like pieces, such strips can be gripped more satisfactorily by the individual small upper jaws 24 of the right hand clamp than would be the case with a clamp having a single upper jaw as long as the lower clamp member l4.

While I have illustrated and described with particularity only a single preferred form of my invention, I do not desire to be limited to the exact details thus illustrated and described, but intend to cover all forms and arrangements that come within the definitions of my invention constituting the appended claims.

I claim:

1. The method of manipulating a sheet to polish an entire face thereof with a rotatable polishing element capable of spanning the width of the sheet: which consists in bringing one end of the sheet into engagement with the polishing element and feeding the sheet throughout its entire length past said polishing element, meanwhile gripping the sheet at its second end until that end is near the said element, then gripping the sheet at a point beyond said element and releasing the grip on the second end, moving the sheet back toward the starting point without first releasing the existing grip, again gripping the second end of the sheet when that end has moved back past said polishing element and, lastly, releasing the other grip.

2. The method of handling a sheet in a polishing machine provided with a bed at least as long as the sheet and reciprocable under a polishing element over a distance greater than the length of the sheet: which consists in laying the sheet on one end of the bed, moving the bed in the direction to carry the inner end of the sheet past said element while gripping the outer end of the sheet and compelling the sheet to travel with the bed, gripping the sheet at a point beyond said element before the outer end thereof reaches said element, then releasing the grip on said outer end and allowing the bed to continue its movement until said outer end has passed said element; then reversing the direction of travel of the bed, gripping the outer endof the sheet again after that end has moved back past the polishing element and, finally, releasing the grip on the sheet beyond-said element.

3. The combination with a polishing machine provided with a polishing element and a reciprocable bed to carry a sheet to be polished back and forth under said element: of a clamp for the sheet on one end of said bed and movable a limited distance lengthwise of the bed, a stop to arrest the movement of the clamp short of said polishing element as the bed travels a distance greater than that required to carry the clamp beyond the element, means to open said clamp as it nears said stop, a second clamp for securing the sheet to the bed at a point beyond the polishing element, and means to close the second clamp before the first clamp opens.

4. The combination with a polishing machine provided with a rotatable polishing element and a reciprocable bed to carry a sheet to be polished back and forth under said element: of a clamp for the sheet on one end of said bed and movable a limited distance lengthwise of the bed, yieldable means tending constantly to hold the clamp at the inner limit of said movement, a stop in the path of the clamp short of said polishing element, means to open said clamp as it nears said stop, a second clamp for securing the sheet to the bed at a point beyond the polishing element, and means to close the second clamp before the first clamp opens.

5. The combination with a polishing machine provided with a rotatable polishing element and a reciprocable bed to carry a sheet to be polished back and forth under said element: of a clamp for the sheet on one end of said bed and movable a limited distance lengthwise of the bed, a stop arresting the movement of the clamp short of said polishing element while the bed continues to move in the same direction, means to open said clamp as it nears said stop and again close it after the bed has made a return movement to its position at the time the clamp reaches the stop, a second clamp for securing the sheet to the bed at a point beyond the polishing element, and means to close the second clamp before the first clamp opens and open it again after the first clamp closes.

6. A machine as set forth in claim 5, wherein the greater portion of the bed is in the form of a thin panel, and wherein the second clamp is provided with two jaws that extend across the machine at right angles to the direction of travel of the bed, one below and the other above the thin panel portion of the bed.

7. The combination with a polishing machine provided with a polishing element and a reciprocable bed to carry a sheet to be polished back and forth under said element: of a clamp for the outer end of a sheet on the bed on and slidable lengthwise of the bed between a working position and an idle position wherein it is clear of the polishing element when the outer end of the sheet is carried past the polishing element, means yieldingly holding the clamp in the working position, means to shift said clamp into its idle position at a predetermined point in the inward movement of the bed and to permit it to return to its working position when the bed returns to that point, means to open said clamp shortly before said point is reached on the inward stroke of the bed and shortly after that point is reached on the return stroke of the bed, a second clamp beyond the polishing element and movable toward and away from the polishing element, and means to close the second clamp on the sheet and bed before the first clamp opens andv to open the second clamp after the first clamp closes.

8. The combination with a polishing machine provided with a polishing element and a reciprocable bed to carry a sheet to be polished back and forth under said element: of a clamp for the outer end of a sheet on the bed movable on the bed between a working position and an idle position wherein it is clear of the polishing element when the outer end of the sheet is carried past the polishing element, means to shift said clamp into its idle position at a predetermined point in the inward movement of the bed, means to open said clamp shortly before said point is reached, a second clamp beyond the polishing element and movable toward and away from the polishing element, and means to close the second clamp on the sheet and bed before the first clamp opens as aforesaid.

9. The combination with a polishing machine provided with a bed adapted to reciprocate from a position at one end of the machine through a polishing zone remote from said end: of a sheetengaging clamp on the outer end of and movable lengthwise of the bed, a second clamp slidably mounted on a stationary part of the machine a little beyond the polishing zone, the second clamp comprising a part underlying the bed and a part above the bed cooperating to clamp between them the bed and a sheet lying on the bed, yieldable means resisting movements of the clamps on their supports in directions away from the polishing zone, a stop in position to arrest the movement of the first clamp after it has moved with the bed toward the polishing zone to a predetermined point; and an actuating system, including switches operated by the bed, that closes the second clamp before the first clamp reaches the stop and then opens the second clamp, and, on the reverse movement of the bed, closes the first clamp and then opens the second clamp.

10. The combination with a polishing machine provided with a bed adapted to reciprocate from a position at one end of the machine through a polishing zone remote from said end: of a sheet-engaging clamp on the outer end of and movable lengthwise of the bed, a second clamp slidably mounted on a stationary part of the machine a little beyond the polishing zone, the second clamp comprising a part underlying the bed and a part above the bed cooperating to clamp between them the bed and a sheet lying on the bed, yieldable means resisting movements of the clamps on their supports in directions away from the polishing zone, a stop to arrest the movement of the first clamp after it has moved with the bed toward the polishing zone to a predetermined point, pneumatic actuators for said clamps; and an electric control system for said actuators, including switches mounted on a stationary part of the machine and switch trippers on the bed to close the second clamp be- 11 fore the first clamp reaches the stop and then open the second clamp, and, on the reverse movement of the bed, to close the first clamp and then open the second clamp.

11. The combination as set forth in claim 10, wherein the control system contains a push button to cause the first clamp to open and another push button to cause that clamp to close.

12. The combination with the reciprocating bed of a sheet polishing machine, of a lower clamp jaw in the form of a stiff plate extending across the width of and supported by the bed near one end of the latter, a plurality of upper jaw members extending in parallel, spaced relation lengthwise of the machine above said plate, means connecting the upper jaws to said plate for rocking movements about a common transverse axis near the inner ends of the upper jaws, and individual pneumatic actuators for said upper jaws to close them against the lower jaw and hold them closed.

13. The combination as set forth in claim 12, wherein the actuators are connected to a single manifold and a valve having a, conduit to supply air under pressure is connected to the manifold.

14. The combination as set forth in claim 12,

wherein the lower clamp jaw is slidable length wise of the bed, a pair of cushions in the form of pistons connected to that jaw extending into cylinders extending lengthwise of the machine, wherein there is a source of air under pressure connected directly with the interiors of the corresponding ends of the cylinders, and wherein there is a valved connection between said source of air under pressure and the actuators for the upper clamp jaws.

RUBIN CHAPLIK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,024,628 Grover Apr. 30, 1912 1,223,040 Devanney Apr. 1'7, 1917 1,298,999 Moltrup Apr. 1, 1919 1,904,947 Leech Apr. 18, 1933 1,973,801 Dustan Sept. 18, 1934 2,019,889 Breed Nov. 5, 1935 2,264,508 Carson Dec. 2, 1941 2,436,960 Fassnacht Mar. 2, 1948 

